Lead Tetraacetate In Benzene Research Articles

Cleavage of (octaethyl-2,3-dihydroxychlorinato)nickel(II) to give the novel 2,3-dioxo-2,3-secochlorin system

Treatment of (octaethyl-2,3-dihydroxychlorinato)nickel(II) with lead tetraacetate in benzene causes cleavage of the 2–3 bond to give the nickel(II) 2,3-secochlorin-2,3-dione system 7, a previously unknown structural type. The structure is established by elemental analysis and spectroscopic methods, and confirmed by X-ray analysis. The dione gives a bis(2,4-dinitrophenylhydrazone). Treatment with base causes an aldol-type condensation to occur to give the (2-oxo-2a-homoporphyrinato)nickel(II) 8. This substance is rather unreactive, and it has not been possible to prepare carbonyl derivatives. This lack of reactivity is rationalised in terms of charge delocalisation which reduces carbonyl double-bond character. These novel pathways are discussed in relation to the known (and different) pathways of chlorophyll catabolism which have recently been uncovered.

Free Sphingosine in Human Epidermis

The aim of the present study is to determine the concentration and composition of free long-chain bases in human stratum corneum. Samples of foot callus obtained from a local chiropodist were extracted at room temperature with chloroform: methanol mixtures (2:1, 1:1, and 1:2). The extracts were concentrated, filtered to remove nonlipid debris, and dissolved in chloroform: methanol, 2:1, at a concentration of 25 mg/ml. Small portions of extract were treated with 2,4-dinitrofluorobenzene to convert free amino groups to N-dinitrophenyl derivatives, which were subsequently separated from other components by thin-layer chromatography (TLC) and quantitated by photodensitometry at a wave-length of 355 nm. The N-dinitrophenylsphingosines were then isolated by preparative TLC and oxidized with lead tetraacetate in benzene to produce aldehydes, which were analyzed by gas-liquid chromatography. It was found that callus lipid contained 3.39 +/- 0.57 mg free sphingosine, 1.60 +/- 0.72 mg dihydrosphingosine and traces of phytosphingosine per g lipid. The sphingosines and dihydrosphingosines ranged from 16 through 20 carbons in length, with 18:1 as the predominant constituent. These findings are similar to those recently reported for pig epidermis and support the possible role of free sphingosine as a regulator of epidermal differentiation.

Synthetic approaches to glutinosone

AbstractThe dienone 4 was converted to ketal ketone 6 by ketalization and reduction with lithium in liquid ammonia. The tosylhyrazone of 6, on treatment with lithium diisopropylamide, afforded the olefin 9 which was converted to the bromohydrin 12 with N‐bromosuccinimide. Oxidation of bromohydrin 12 with lead tetraacetate in benzene afforded the bromo ether 16, whose transformation to epoxy ketone 3 was achieved by heating with tri‐n‐butyltin hydride in methanol followed by deketalization.

Organotin and -mercury routes to enones, dienones amd spiroacetals

Conjugate addition of trinethyltinlithium to cyclohex-2-enone followed by enolate trapping with alkylating agents provide traus-2-alkyl-3-trimethylstannylcyclohexanones, which on reaction with Grignard reagents derived from 4-bromo-1-butene or 5-bromo-1-pentene afford tertiary γ-stannylcyclohexanols in a highly diastereoselective fashion. Triaethylstannyl-triggered ring fragmentation (by lead tetraacetate in benzene) leads efficiently to dienones, which on hydroxymercuration, cyclisation and reduction provide a range of 1,6-dioxaspiro[4.5]decanes and 1,7-dioxaspiro[5,5]undecanes, some of which are of insect origin. Epoxidation of these dienones, followed by acid catalysed hydrolysis and cyclisation leads to hydroxy substituted spiroacetals. Syntheses of 6-oxononan-1-ol (a glandular component of the fruit flies, D. halfordiae and D. occipitalis) and E-6-nonene-2-one, which is transformed readily into exo or endo-brevicomin, are also presented. Some dialkyl substituted [4.5]- and [5.5] spiroacetals have been acquired also by free radical addition reactions etc., utilising organomercury chemistry.

Improved synthesis of anti-sesquinorbornene

Treatment of methyl hydrogen decahydro-1,4:5,8-exo,endo-dimethanonaphthalene-4a,8a-dicarboxylate with lead tetraacetate in benzene – acetic acid replaces the carboxyl group by an acetoxy group. Hydrolysis of this product with 25% sulfuric acid at 130 °C forms 8a-hydroxydecahydro-1,4:5,8-exo,endo-dimethanonaphthalene-4a-carboxylic acid 10. The reaction between 10 and benzenesulfonyl chloride in pyridine containing triethylamine at 95 °C produces anti-sesquinorbornene 1 in 34% yield. In the absence of triethylamine 1 is converted to the hydrochloride. The iodohydroperoxide of 1 is converted by silver acetate at 0 °C to the diketone in a luminescent reaction. The 1,2-dioxetane could not be isolated. Decahydro-1,4:5,8-exo,exo-dimethanonaphthalene-4a,8a-dicarboxylic anhydride is converted slowly by methoxide ion in methanol at 150 °C to the monomethyl ester which then undergoes demethylation. The isomeric exo,endo anhydride undergoes reaction readily with methoxide ion at 80 °C.

Lead Tetraacetate Oxidation of Humulene and Conformational Analysis of the Produced Humulatrienediols

Abstract Humulene was oxidized by lead tetraacetate in benzene to give 2,5,9-humulatrien-7-ol acetate and 1,5,9-humulatriene-3,7-diol diacetates. Conformational analysis of 1,5,9-humulatriene-3,7-diols was performed by NMR spectroscopy and molecular mechanics calculations.

Factors affecting the stability and equilibria of free radicals. Part 11. 1-Benzoyl-2,2-bis-(3,5-di-t-butylphenyl)hydrazyl and its temperature-dependent electron spin resonance spectrum

The title free radical was prepared by oxidizing the corresponding hydrazine with lead tetra-acetate in benzene or toluene. Its e.s.r. spectrum undergoes reversible changes in the temperature range –90 to +60 °C. Simulated e.s.r. spectra indicate that the two di-t-butylphenyl groups are non-equivalent owing to restricted rotation around the N–N bond at low temperatures, but at 60 °C these two aryl groups become equivalent. The ΔG‡ value of the rotation barrier is about 31 kJ mol–1 in the temperature range –30 to +50 °C.

ChemInform Abstract: REACTION OF (20S)‐3β‐ACETOXYBISNORCHOL‐5‐ENIC ACID WITH LEAD TETRAACETATE; STRUCTURE OF PREGNANE DERIVATIVES AND A DIMER

AbstractDie Oxidation der Säure (I) mit Bleitetraacetat wird unter verschiedenen Reaktionsbedingungen und in verschiedenen Lösungsmitteln untersucht und führt zu den Produkten (II)‐(VIII), deren Strukturen zugeordnet werden.

Reaction of (20S)-3.BETA.-acetoxybisnorchol-5-enic acid with lead tetraacetate. Structure of pregnane derivatives and a dimer.

Reaction of 3β-acetoxybisnorchol-5-enic acid (1) with lead tetraacetate in benzene gave ⊿20 and ⊿17 (20) compounds (2a and 2b) and 20α-and 20β-acetoxy compounds (3a and 3b), with a trace of 20-keto compound (4) and a dimer (5). The structure of 5 was determined as 3'β-acetoxypregn-5'-en-20'α-yl 3β-acetoxybisnorchol-5-enate (Chart 1). The use of toluene or xylene in place of benzene resulted in decreased formation of 2b with the formation of the 17-ethyl compound (2c). The reactions were examined under various conditions (Table I) and the reaction mechanisms are discussed.

ChemInform Abstract: THE REACTION OF LEAD TETRAACETATE WITH 3β‐HYDROXY STEROIDS

Abstract3β‐Hydroxysteroide wie z.B. die Verbindungen (I) und (III) mit elektronegativer Substitution der 5a‐Stellung werden durch Bleitetraacetat in Gegenwart von Calciumcarbonat und einer Spur Benzoylperoxid zu 3β,19‐Oxidosteroiden (II) und (IV) oxidiert.

The constituents of Schizandra chinensis Baill. IX. The cleavage of the methylenedioxyl moiety with lead tetraacetate in benzene, and the structure of angeloylgomisin Q.

A procedure for selective cleavage of the methylenedioxyl moiety with lead tetraacetate in dry benzene is described. Piperonylic acid methyl ester (5), 4-nitro-1, 2-methylenedioxybenzene (6), 3, 4-methylenedioxytoluene (7), 2, 3-methylenedioxyanisole (8) and gomisin A (9) afforded protocatechuic acid (12), 4-nitrocatechol (13), 3, 4-dihydroxytoluene (14), 2, 3-dihydroxyanisole (15) and compound 16, respectively. The structure of angeloylgomisin Q isolated from the fruits of Schizandra chinensis BAILL. (Schizandraceae), was elucidated as 1 by using the above reaction.

The reaction of lead tetraacetate with 3.BETA.-hydroxy steroids.

It was found that the reaction of lead tetraacetate with 3β-hydroxy steroids of the 5α-series gave the corresponding 3β, 19-oxido steroids. Only poor yields were obtained in the cases of 3β-hydroxy steroids having no substituent at C-5 (5α-H). Substitution at the 5α-position by an electronegative group such as halogen or acetoxyl enhanced the yield of the 3β, 19-oxido compound. The best result was obtained when a steroid was heated with lead tetraacetate in benzene in the presence of calcium carbonate and a trace of benzoyl peroxide.

TRANSFORMATION OF GRAYANOTOXIN II TETRAACETATE TO A 1,5-SECOGRAYANANE DERIVATIVE

Abstract Irradiation of grayanotoxin II tetraacetate with UV light in the presence of lead tetraacetate in benzene afforded 1-epi-grayanol A pentaacetate in high yield.

The constituents of Schizandra chinensis Baill. The cleavage of the methylenedioxy moiety with lead tetraacetate in benzene, and the structure of angeloylgomisin Q.

The constituents of Schizandra chinensis Baill. The cleavage of the methylenedioxy moiety with lead tetraacetate in benzene, and the structure of angeloylgomisin Q.

Oxidative decarboxylation of the 3-methyl-2-carboxynorbornanes with lead tetraacetate

The mixtures of isomeric acetates produced by oxidative decarboxylation of the four 3-methyl-norbornane-2-carboxylic acids with lead tetraacetate in benzene have been characterized. The composition of these products depends primarily on the configuration of the methyl group in the starting material. The results are compared with those found for the Pb(OAc)4 decarboxylation of the norbornane-, bornane-, and 2,3,3-trimethylnorbornane-2-carboxylic acids. The formation of the products is interpreted in terms of competitive cationic and SNi substitution.

The mechanism of lead tetraacetate decarboxylation. I. Tertiary carboxylic acids

The reactions of cis- and trans-decalin-9-carboxylic acid, 2,2,3-trimethylbutanoic acid, and adamantane-1-carboxylic acid with lead tetraacetate in benzene and, in some cases, acetic acid have been studied. In each case the nature and distribution of the products is consistent with the hypothesis that the reaction mechanism involves the initial generation of tertiary radicals which are subsequently converted into the related cations either by one-electron oxidation by lead species, or via organolead intermediates which undergo heterolysis. The change in product distribution which occurs when the reactions are conducted in the presence of copper salts indicates that tertiary radicals react rapidly with cupric species to afford organocopper intermediates from which olefins are derived by a cis-elimination process, and acetates by SNi or heterolytic mechanisms.

The camphenehydro (methylcamphenilyl) and isobornyl (bornyl) cations. III. Oxidative decarboxylation of carboxylic acids with lead tetraacetate

The oxidative decarboxylation of exo- and endo-bornane-2-carboxylic acid, exo- and endo-2,3,3- trimethylnorbornane-2-carboxylic acid and a-campholenylcarboxylic acid [3-(2',2',3'-trimethyl- cyclopent-3'-eny1)propanoic acid] with lead tetraacetate in benzene and dimethyl sulphoxide (each containing pyridine) in the presence, and absence, of cupric acetate has been investigated. The mode of formation of almost all the products can be satisfactorily rationalized in terms of the initial generation of radicals. In the case of exo- and endo-bornane-2-carboxylic acid, the derived bornyl radical forms organolead and organocopper derivatives that decompose in three ways: (1) by heterolysis by the direct route to give the equilibrating isobornyl and camphenehydro cations, (2) by a cyclic cis-elimination to give bornylene and (3) by an SNi process to give isobornyl and bornyl acetates. exo- and endo-2,3,3-Trimethylnorbornane-2-carboxylic acid yield the 2,3,3-trimethyl- norborn-2-yl radical which is converted into the equilibrating camphenehydro and isobornyl cations either by one-electron oxidation by lead species or via organolead or organocopper derivatives which undergo heterolysis. Processes involving cyclic cis-elimination and SNi substitution may also operate in the organometallic derivatives derived from the tertiary radical. a-Campholenylcarboxylic acid yields the a-campholenyl radical which, in the absence of cupric acetate, undergoes in the main cyclization to give the 2,3,3-trimethylnorbornyl radical. The resulting mixture of products is similar to that obtained from exo- and endo-2,3,3-trimethylnorbornane-2- carboxylic acid. In the presence of cupric acetate, the a-campholenyl radical is trapped at least to the extent of 50% in benzene and 80% in dimethyl sulphoxide to give the corresponding organo- copper derivative which undergoes a cyclic elimination to give 2,3,3-trimethyl-4-vinylcyclopentene and may undergo heterolysis by the x-route to give the camphenehydro and isobornyl cations. A marked change in the composition of the products on changing the solvent from benzene to dimethyl sulphoxide is observed only in the case of a-campholenylcarboxylic acid in the presence of cupric acetate.

The mechanism of lead tetraacetate decarboxylation. II. 2,3,3-Trimethylbutanoic and Adamantane-2-carboxylic acids

Oxidative decarboxylation of 2,3,3-trimethylbutanoic acid with lead tetraacetate in benzene or acetic acid affords mainly 3,3-dimethylbut-2-yl acetate; the major product from the cupric salt catalysed reaction is 3,3-dimethylbut-1-ene. The low yields detected of rearrangement products provide evidence for the intermediacy of organolead and organocopper compounds which decompose by SNi displacement or cyclic cis-elimination. Other reactions discussed are oxidative decarboxylation of adamantane-2-carboxylic acid, deamination of 3,3-dimethylbut-2-ylamine, and thermolysis of bis(2,3,3-trimethylbutanoyl) peroxide and of t-butyl adamantane-2-percarboxylate. A reinterpretation of previous results on the oxidative decarboxylation of exo- and endo-nor- bornane-2-carboxylic acid with lead tetraacetate is presented.

Oxidation of 3-carene with Pb(OAc)4 in benzene

The products of the oxidation of 3-carene with lead tetraacetate in benzene contain, besides the previously identified compounds, also the acetates of trans-4-caren-3-ol, m-mentha-1,3-dien-8-ol and 2-(m-tolyl)-2-propanol, which serves to confirm the assumption that the given reaction proceeds in two directions: a) with the formation of the allylic organolead derivative; and b) of the adduct of 3-carene with Pb(OAc)4, as intermediate products.

Studies on Conformation and Reactivity. X. The Synthesis and Transannular Cyclization of 17β-Benzoyloxy-2α-hydroxy-5β-androstane leading to 17β-Benzoyloxy-2α, 9α-epoxy-5β-androstane

17β-Benzoyloxy-2α-hydroxy-5β-androstane (XIb), the key intermediate for the transannular cyclization reaction from 2C to 9C in the 5β-androstane system, was synthesized from testosterone (III) in six steps and in the overall yield of 17.6% via the intermediacy of 2α-hydroxy-4-en-3-oxo system (VII). The stereochemistry of the epoxidation of the 4-en-3-oao system (III) with alkaline hydrogen peroxide was established, the reaction favoring the formation of the 4β, 5-epoxide (IVb) to the formation of the 4α, 5-isomer (IVa) in the relative ratio of 5:1. Meanwhile, oxidation of XIb with Jones reagent afforded the 2-oxo-5β system (XIIIb) which exhibits negative Cotton effect curves with much weaker intensity compared with that of positive Cotton effect curves exhibited by the 2-oxo-5α system (XIIIa).Treatment of XIb with lead tetraacetate in benzene afforded 17β-benzoyloxy-2α, 9α-epoxy-5β-androstane (XVII). The 17β-acetoxy analogue (XIX) of the 2α, 9α-epoxide (XVII) was converted to the 9α, 11α-epoxide system (XXII) via the 9 (11)-eno intermediate (XXI). Reductive cleavage of XXII with lithium-ethylamine afforded the 2α, 9α, -17β-trihydroxy-5β-androstane (XXIII) which gave 2α, 17β-diacetate (XXIV).